/*******************************************************************************
 * Copyright (c) 2009, 2012 Mountainminds GmbH & Co. KG and Contributors
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    Marc R. Hoffmann - initial API and implementation
 *    
 *******************************************************************************/
package com.laud.doodo.string;
/**
 * CRC64 checksum calculator based on the polynom specified in ISO 3309. The
 * implementation is based on the following publications:
 * 
 * <ul>
 * <li>http://en.wikipedia.org/wiki/Cyclic_redundancy_check</li>
 * <li>http://www.geocities.com/SiliconValley/Pines/8659/crc.htm</li>
 * </ul>
 */
public final class CRC64 {
	//private static final long POLY64REV = 0xd800000000000000L;
	private static final long[] LOOKUPTABLE = new long[] { 0x0L,
			0x1b0000000000000L, 0x360000000000000L, 0x2d0000000000000L,
			0x6c0000000000000L, 0x770000000000000L, 0x5a0000000000000L,
			0x410000000000000L, 0xd80000000000000L, 0xc30000000000000L,
			0xee0000000000000L, 0xf50000000000000L, 0xb40000000000000L,
			0xaf0000000000000L, 0x820000000000000L, 0x990000000000000L,
			0x1b00000000000000L, 0x1ab0000000000000L, 0x1860000000000000L,
			0x19d0000000000000L, 0x1dc0000000000000L, 0x1c70000000000000L,
			0x1ea0000000000000L, 0x1f10000000000000L, 0x1680000000000000L,
			0x1730000000000000L, 0x15e0000000000000L, 0x1450000000000000L,
			0x1040000000000000L, 0x11f0000000000000L, 0x1320000000000000L,
			0x1290000000000000L, 0x3600000000000000L, 0x37b0000000000000L,
			0x3560000000000000L, 0x34d0000000000000L, 0x30c0000000000000L,
			0x3170000000000000L, 0x33a0000000000000L, 0x3210000000000000L,
			0x3b80000000000000L, 0x3a30000000000000L, 0x38e0000000000000L,
			0x3950000000000000L, 0x3d40000000000000L, 0x3cf0000000000000L,
			0x3e20000000000000L, 0x3f90000000000000L, 0x2d00000000000000L,
			0x2cb0000000000000L, 0x2e60000000000000L, 0x2fd0000000000000L,
			0x2bc0000000000000L, 0x2a70000000000000L, 0x28a0000000000000L,
			0x2910000000000000L, 0x2080000000000000L, 0x2130000000000000L,
			0x23e0000000000000L, 0x2250000000000000L, 0x2640000000000000L,
			0x27f0000000000000L, 0x2520000000000000L, 0x2490000000000000L,
			0x6c00000000000000L, 0x6db0000000000000L, 0x6f60000000000000L,
			0x6ed0000000000000L, 0x6ac0000000000000L, 0x6b70000000000000L,
			0x69a0000000000000L, 0x6810000000000000L, 0x6180000000000000L,
			0x6030000000000000L, 0x62e0000000000000L, 0x6350000000000000L,
			0x6740000000000000L, 0x66f0000000000000L, 0x6420000000000000L,
			0x6590000000000000L, 0x7700000000000000L, 0x76b0000000000000L,
			0x7460000000000000L, 0x75d0000000000000L, 0x71c0000000000000L,
			0x7070000000000000L, 0x72a0000000000000L, 0x7310000000000000L,
			0x7a80000000000000L, 0x7b30000000000000L, 0x79e0000000000000L,
			0x7850000000000000L, 0x7c40000000000000L, 0x7df0000000000000L,
			0x7f20000000000000L, 0x7e90000000000000L, 0x5a00000000000000L,
			0x5bb0000000000000L, 0x5960000000000000L, 0x58d0000000000000L,
			0x5cc0000000000000L, 0x5d70000000000000L, 0x5fa0000000000000L,
			0x5e10000000000000L, 0x5780000000000000L, 0x5630000000000000L,
			0x54e0000000000000L, 0x5550000000000000L, 0x5140000000000000L,
			0x50f0000000000000L, 0x5220000000000000L, 0x5390000000000000L,
			0x4100000000000000L, 0x40b0000000000000L, 0x4260000000000000L,
			0x43d0000000000000L, 0x47c0000000000000L, 0x4670000000000000L,
			0x44a0000000000000L, 0x4510000000000000L, 0x4c80000000000000L,
			0x4d30000000000000L, 0x4fe0000000000000L, 0x4e50000000000000L,
			0x4a40000000000000L, 0x4bf0000000000000L, 0x4920000000000000L,
			0x4890000000000000L, 0xd800000000000000L, 0xd9b0000000000000L,
			0xdb60000000000000L, 0xdad0000000000000L, 0xdec0000000000000L,
			0xdf70000000000000L, 0xdda0000000000000L, 0xdc10000000000000L,
			0xd580000000000000L, 0xd430000000000000L, 0xd6e0000000000000L,
			0xd750000000000000L, 0xd340000000000000L, 0xd2f0000000000000L,
			0xd020000000000000L, 0xd190000000000000L, 0xc300000000000000L,
			0xc2b0000000000000L, 0xc060000000000000L, 0xc1d0000000000000L,
			0xc5c0000000000000L, 0xc470000000000000L, 0xc6a0000000000000L,
			0xc710000000000000L, 0xce80000000000000L, 0xcf30000000000000L,
			0xcde0000000000000L, 0xcc50000000000000L, 0xc840000000000000L,
			0xc9f0000000000000L, 0xcb20000000000000L, 0xca90000000000000L,
			0xee00000000000000L, 0xefb0000000000000L, 0xed60000000000000L,
			0xecd0000000000000L, 0xe8c0000000000000L, 0xe970000000000000L,
			0xeba0000000000000L, 0xea10000000000000L, 0xe380000000000000L,
			0xe230000000000000L, 0xe0e0000000000000L, 0xe150000000000000L,
			0xe540000000000000L, 0xe4f0000000000000L, 0xe620000000000000L,
			0xe790000000000000L, 0xf500000000000000L, 0xf4b0000000000000L,
			0xf660000000000000L, 0xf7d0000000000000L, 0xf3c0000000000000L,
			0xf270000000000000L, 0xf0a0000000000000L, 0xf110000000000000L,
			0xf880000000000000L, 0xf930000000000000L, 0xfbe0000000000000L,
			0xfa50000000000000L, 0xfe40000000000000L, 0xfff0000000000000L,
			0xfd20000000000000L, 0xfc90000000000000L, 0xb400000000000000L,
			0xb5b0000000000000L, 0xb760000000000000L, 0xb6d0000000000000L,
			0xb2c0000000000000L, 0xb370000000000000L, 0xb1a0000000000000L,
			0xb010000000000000L, 0xb980000000000000L, 0xb830000000000000L,
			0xbae0000000000000L, 0xbb50000000000000L, 0xbf40000000000000L,
			0xbef0000000000000L, 0xbc20000000000000L, 0xbd90000000000000L,
			0xaf00000000000000L, 0xaeb0000000000000L, 0xac60000000000000L,
			0xadd0000000000000L, 0xa9c0000000000000L, 0xa870000000000000L,
			0xaaa0000000000000L, 0xab10000000000000L, 0xa280000000000000L,
			0xa330000000000000L, 0xa1e0000000000000L, 0xa050000000000000L,
			0xa440000000000000L, 0xa5f0000000000000L, 0xa720000000000000L,
			0xa690000000000000L, 0x8200000000000000L, 0x83b0000000000000L,
			0x8160000000000000L, 0x80d0000000000000L, 0x84c0000000000000L,
			0x8570000000000000L, 0x87a0000000000000L, 0x8610000000000000L,
			0x8f80000000000000L, 0x8e30000000000000L, 0x8ce0000000000000L,
			0x8d50000000000000L, 0x8940000000000000L, 0x88f0000000000000L,
			0x8a20000000000000L, 0x8b90000000000000L, 0x9900000000000000L,
			0x98b0000000000000L, 0x9a60000000000000L, 0x9bd0000000000000L,
			0x9fc0000000000000L, 0x9e70000000000000L, 0x9ca0000000000000L,
			0x9d10000000000000L, 0x9480000000000000L, 0x9530000000000000L,
			0x97e0000000000000L, 0x9650000000000000L, 0x9240000000000000L,
			0x93f0000000000000L, 0x9120000000000000L, 0x9090000000000000L };

	/*
	static {
		LOOKUPTABLE = new long[0x100];
		for (int i = 0; i < 0x100; i++) {
			long v = i;
			for (int j = 0; j < 8; j++) {
				if ((v & 1) == 1) {
					v = (v >>> 1) ^ POLY64REV;
				} else {
					v = (v >>> 1);
				}
			}
			LOOKUPTABLE[i] = v;
		}
	}*/

	/**
	 * Calculates the CRC64 checksum for the given data array.
	 * 
	 * @param data
	 *            data to calculate checksum for
	 * @return checksum value
	 */
	public static long checksum(final byte[] data) {
		long sum = 0;
		for (int i = 0; i < data.length; i++) {
			final int lookupidx = ((int) sum ^ data[i]) & 0xff;
			sum = (sum >>> 8) ^ LOOKUPTABLE[lookupidx];
		}
		return sum;
	}

	private CRC64() {
	}
}